Abstract
We used above- and below-water radiometry measurements collected during a research voyage in the eastern Indian Ocean to assess uncertainties in deriving the remote sensing reflectance, Rrs, from unattended above-water radiometric data collection with the In-Situ Marine Optics Pty. Ltd. (IMO) Dynamic Above-water Radiance (L) and Irradiance (E) Collector (DALEC). To achieve this, the Rrs values derived from using the latest version of this hyperspectral radiometer were compared to values obtained from two in-water profiling radiometer systems of rather general use in the ocean optics research community, i.e., the Biospherical Instruments Inc. Compact Optical Profiling System (C-OPS) and the Seabird HyperPro II. Our results show that unattended, carefully quality-controlled, DALEC measurements provide Rrs for wavelengths < 600 nm that match those derived from the in-water systems with no bias and a dispersion of about 8%, provided that the appropriate technique is used to quantify the contribution of sky light reflection to the measured signal. The dispersion is larger (25-50%) for red bands, which is expected for clear oligotrophic waters as encountered during the voyage, where ∼2 10-5 < Rrs < ∼2 10-4 sr-1. For comparison, the two in-water systems provided Rrs in agreement within 4% for wavelengths < 600 nm.
Highlights
Producing reliable geophysical products from satellite ocean color radiometry (OCR) requires a sustained effort to collect validation data in the field [1,2]
The FRM definition is that of a suite of independent, fully characterized, and traceable ground measurements that follow the guidelines outlined by the Group on Earth Observations (GEO) / Committee on Earth Observation Satellites (CEOS) Quality Assurance framework for Earth Observation (QA4EO)
Examples of full Es and Lw spectra from the DALEC and HyperPro plus the values for the discrete spectral bands of the Compact Optical Profiling System (C-OPS) are displayed in Fig. 6 for station 11
Summary
Producing reliable geophysical products from satellite ocean color radiometry (OCR) requires a sustained effort to collect validation data in the field [1,2]. Ensuring consistency of the data contributed to these archives is challenging, and significant effort is put in quality controlling the submitted data Still, it cannot be ascertained whether all submitted data were collected following recommended data acquisition protocols, and what processing steps were followed when deriving quantities such as Rrs from basic radiometric quantities. It cannot be ascertained whether all submitted data were collected following recommended data acquisition protocols, and what processing steps were followed when deriving quantities such as Rrs from basic radiometric quantities Recognizing this difficulty inherent to collating data from multiple users, and aiming at improving consistency among data used for validation purposes, the international research community and space agencies defined the concept of Fiducial Reference Measurements (FRM, [6]). The FRM definition is that of a suite of independent, fully characterized, and traceable ground measurements that follow the guidelines outlined by the Group on Earth Observations (GEO) / Committee on Earth Observation Satellites (CEOS) Quality Assurance framework for Earth Observation (QA4EO)
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